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The role of spontaneous effort during mechanical ventilation: normal lung versus injured lung.

Yoshida T, Uchiyama A, Fujino Y - J Intensive Care (2015)

Bottom Line: Thus, increased transpulmonary pressure provides various benefits for gas exchange, ventilation pattern, and lung aeration.Thus, during the early stages of severe ARDS, the strict control of transpulmonary pressure and prevention of Pendelluft should be achieved with the short-term use of muscle paralysis.When there is preserved spontaneous effort in ARDS, spontaneous effort should be maintained at a modest level, as the transpulmonary pressure and the effect size of Pendelluft depend on the intensity of the spontaneous effort.

View Article: PubMed Central - PubMed

Affiliation: Intensive Care Unit, Osaka University Hospital, 2-15 Yamadaoka, Suita, Osaka 565-0871 Japan.

ABSTRACT
The role of preserving spontaneous effort during mechanical ventilation and its interaction with mechanical ventilation have been actively investigated for several decades. Inspiratory muscle activities can lower the pleural components surrounding the lung, leading to an increase in transpulmonary pressure when spontaneous breathing effort is preserved during mechanical ventilation. Thus, increased transpulmonary pressure provides various benefits for gas exchange, ventilation pattern, and lung aeration. However, it is important to note that these beneficial effects of preserved spontaneous effort have been demonstrated only when spontaneous effort is modest and lung injury is less severe. Recent studies have revealed the 'dark side' of spontaneous effort during mechanical ventilation, especially in severe lung injury. The 'dark side' refers to uncontrollable transpulmonary pressure due to combined high inspiratory pressure with excessive spontaneous effort and the injurious lung inflation pattern of Pendelluft (i.e., the translocation of air from nondependent lung regions to dependent lung regions). Thus, during the early stages of severe ARDS, the strict control of transpulmonary pressure and prevention of Pendelluft should be achieved with the short-term use of muscle paralysis. When there is preserved spontaneous effort in ARDS, spontaneous effort should be maintained at a modest level, as the transpulmonary pressure and the effect size of Pendelluft depend on the intensity of the spontaneous effort.

No MeSH data available.


Related in: MedlinePlus

CT images in experimental lung injury—muscle paralysis vs. spontaneous breathing. Both dynamic CT images of the same anatomical, sagittal level at end-expiration are shown to compare the end-expiratory lung volume and the shape of the diaphragm. CT images are colored according to their Hounsfield units densities. The black lines indicate the diaphragm at end-expiration. These dynamic CT images were continuously taken after injection of neuromuscular blocking agent, without any change in ventilatory settings. Spontaneous breathing effort restored the end-expiratory lung volume due to diaphragmatic muscle tone. Once diaphragm was paralyzed, diaphragm shifted to cranial direction, resulting in large collapse in dorsal lung regions. Note that this happened because inadequate (low) PEEP was applied.
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Fig5: CT images in experimental lung injury—muscle paralysis vs. spontaneous breathing. Both dynamic CT images of the same anatomical, sagittal level at end-expiration are shown to compare the end-expiratory lung volume and the shape of the diaphragm. CT images are colored according to their Hounsfield units densities. The black lines indicate the diaphragm at end-expiration. These dynamic CT images were continuously taken after injection of neuromuscular blocking agent, without any change in ventilatory settings. Spontaneous breathing effort restored the end-expiratory lung volume due to diaphragmatic muscle tone. Once diaphragm was paralyzed, diaphragm shifted to cranial direction, resulting in large collapse in dorsal lung regions. Note that this happened because inadequate (low) PEEP was applied.

Mentions: It is important to note that the evidence for beneficial effects of spontaneous breathing has been gathered in normal lungs and less severe forms of ARDS with modest ventilatory demands [2,3,5-7,11]. Spontaneous breathing effort during mechanical ventilation improves gas exchange and has been associated with better lung aeration in CT analysis in experimental and clinical studies with less severe forms of ARDS [2,5-7,11]. The plausible explanation for the beneficial effects of spontaneous effort is the alternation of the pleural compartment surrounding the lung. Gentle inspiratory muscle contractions expand the lung actively, leading to an increase and sustainment in PL [11,28]. Continuous tonic activity of the diaphragm is effective for maintaining end-expiratory lung volume [37]. Paralysis shifts the diaphragm to the cranial direction and increases Ppl, resulting in a significant decrease in the end-expiratory lung volume (Figure 5). A tidal increase in PL during inspiration also achieves homogeneous ventilation. In 2001, Putensen et al. performed a randomized clinical study in trauma patients with acute lung injury (note that subjects were not ARDS) and found that the preserved spontaneous effort during mechanical ventilation improves oxygenation and shortens durations of ventilatory support and ICU stays compared with a muscle paralysis group [2]. Several issues for optimizing the beneficial effects of spontaneous effort during mechanical ventilation should be addressed. First, the plateau pressure that was applied in clinical (and experimental) studies that demonstrated the benefits of spontaneous breathing could be kept relatively low because the lung injury was less severe [2,5-7,11,38]. The review of biphasic positive airway pressure (BIPAP) ventilation (ventilatory mode to facilitate spontaneous breathing effort) performed during the past 24 years demonstrates that plateau pressures applied during BIPAP ventilation is less than 20 cm H2O in patients with ARDS [39]. In contrast, plateau pressures applied in clinical studies showing the beneficial effects of muscle paralysis on severe ARDS were higher (25–27.5 cm H2O), reflecting the severity of ARDS [13-15]. Second, spontaneous effort is generally modest in less severe forms of ARDS, which is evident from the lesser duration and lower amplitude of the negative swings in Ppl that diaphragmatic contraction generates [11].Figure 5


The role of spontaneous effort during mechanical ventilation: normal lung versus injured lung.

Yoshida T, Uchiyama A, Fujino Y - J Intensive Care (2015)

CT images in experimental lung injury—muscle paralysis vs. spontaneous breathing. Both dynamic CT images of the same anatomical, sagittal level at end-expiration are shown to compare the end-expiratory lung volume and the shape of the diaphragm. CT images are colored according to their Hounsfield units densities. The black lines indicate the diaphragm at end-expiration. These dynamic CT images were continuously taken after injection of neuromuscular blocking agent, without any change in ventilatory settings. Spontaneous breathing effort restored the end-expiratory lung volume due to diaphragmatic muscle tone. Once diaphragm was paralyzed, diaphragm shifted to cranial direction, resulting in large collapse in dorsal lung regions. Note that this happened because inadequate (low) PEEP was applied.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4940771&req=5

Fig5: CT images in experimental lung injury—muscle paralysis vs. spontaneous breathing. Both dynamic CT images of the same anatomical, sagittal level at end-expiration are shown to compare the end-expiratory lung volume and the shape of the diaphragm. CT images are colored according to their Hounsfield units densities. The black lines indicate the diaphragm at end-expiration. These dynamic CT images were continuously taken after injection of neuromuscular blocking agent, without any change in ventilatory settings. Spontaneous breathing effort restored the end-expiratory lung volume due to diaphragmatic muscle tone. Once diaphragm was paralyzed, diaphragm shifted to cranial direction, resulting in large collapse in dorsal lung regions. Note that this happened because inadequate (low) PEEP was applied.
Mentions: It is important to note that the evidence for beneficial effects of spontaneous breathing has been gathered in normal lungs and less severe forms of ARDS with modest ventilatory demands [2,3,5-7,11]. Spontaneous breathing effort during mechanical ventilation improves gas exchange and has been associated with better lung aeration in CT analysis in experimental and clinical studies with less severe forms of ARDS [2,5-7,11]. The plausible explanation for the beneficial effects of spontaneous effort is the alternation of the pleural compartment surrounding the lung. Gentle inspiratory muscle contractions expand the lung actively, leading to an increase and sustainment in PL [11,28]. Continuous tonic activity of the diaphragm is effective for maintaining end-expiratory lung volume [37]. Paralysis shifts the diaphragm to the cranial direction and increases Ppl, resulting in a significant decrease in the end-expiratory lung volume (Figure 5). A tidal increase in PL during inspiration also achieves homogeneous ventilation. In 2001, Putensen et al. performed a randomized clinical study in trauma patients with acute lung injury (note that subjects were not ARDS) and found that the preserved spontaneous effort during mechanical ventilation improves oxygenation and shortens durations of ventilatory support and ICU stays compared with a muscle paralysis group [2]. Several issues for optimizing the beneficial effects of spontaneous effort during mechanical ventilation should be addressed. First, the plateau pressure that was applied in clinical (and experimental) studies that demonstrated the benefits of spontaneous breathing could be kept relatively low because the lung injury was less severe [2,5-7,11,38]. The review of biphasic positive airway pressure (BIPAP) ventilation (ventilatory mode to facilitate spontaneous breathing effort) performed during the past 24 years demonstrates that plateau pressures applied during BIPAP ventilation is less than 20 cm H2O in patients with ARDS [39]. In contrast, plateau pressures applied in clinical studies showing the beneficial effects of muscle paralysis on severe ARDS were higher (25–27.5 cm H2O), reflecting the severity of ARDS [13-15]. Second, spontaneous effort is generally modest in less severe forms of ARDS, which is evident from the lesser duration and lower amplitude of the negative swings in Ppl that diaphragmatic contraction generates [11].Figure 5

Bottom Line: Thus, increased transpulmonary pressure provides various benefits for gas exchange, ventilation pattern, and lung aeration.Thus, during the early stages of severe ARDS, the strict control of transpulmonary pressure and prevention of Pendelluft should be achieved with the short-term use of muscle paralysis.When there is preserved spontaneous effort in ARDS, spontaneous effort should be maintained at a modest level, as the transpulmonary pressure and the effect size of Pendelluft depend on the intensity of the spontaneous effort.

View Article: PubMed Central - PubMed

Affiliation: Intensive Care Unit, Osaka University Hospital, 2-15 Yamadaoka, Suita, Osaka 565-0871 Japan.

ABSTRACT
The role of preserving spontaneous effort during mechanical ventilation and its interaction with mechanical ventilation have been actively investigated for several decades. Inspiratory muscle activities can lower the pleural components surrounding the lung, leading to an increase in transpulmonary pressure when spontaneous breathing effort is preserved during mechanical ventilation. Thus, increased transpulmonary pressure provides various benefits for gas exchange, ventilation pattern, and lung aeration. However, it is important to note that these beneficial effects of preserved spontaneous effort have been demonstrated only when spontaneous effort is modest and lung injury is less severe. Recent studies have revealed the 'dark side' of spontaneous effort during mechanical ventilation, especially in severe lung injury. The 'dark side' refers to uncontrollable transpulmonary pressure due to combined high inspiratory pressure with excessive spontaneous effort and the injurious lung inflation pattern of Pendelluft (i.e., the translocation of air from nondependent lung regions to dependent lung regions). Thus, during the early stages of severe ARDS, the strict control of transpulmonary pressure and prevention of Pendelluft should be achieved with the short-term use of muscle paralysis. When there is preserved spontaneous effort in ARDS, spontaneous effort should be maintained at a modest level, as the transpulmonary pressure and the effect size of Pendelluft depend on the intensity of the spontaneous effort.

No MeSH data available.


Related in: MedlinePlus